Pune: State Bank of India - India's largest bank - and its five associates have blocked some 6 lakh debit (ATM) cards following a malware-related security breach. The bank said the move has affected the customers who used their cards at an unspecified number of malware-infected ATMs run by other banks, across the country.

SBI branch managers have been instructed to issue new cards to the customers, free of cost.

In a letter to branch managers across the country, SBI said, "For security reasons, some cards have been blocked. At the customer's request, a new card may be issued free of cost. The existing cards must not be un-blocked."

"It's a security breach, but not in our banks' systems. Many other banks also have this breach, right now and since a long time," Shiv Kumar Bhasin, SBI's chief technology officer, told TOI, adding customers who only used their cards at SBI-run ATMs have not been affected.

"A few bank ATMs have been affected by a malware. When people use their card on infected switches or ATMs, there is a high probability that their data will be compromised," Bhasin said. If customers unaffected so far use their cards at the affected ATMs, there is a likelihood their cards will be compromised too.

"Customers need not panic. They can either approach their branch, call up phone banking or use the internet for 're-carding.' They can also set their PINs from their homes using internet banking," Bhasin said.

"Banks whose ATMs have been infected must come forward and declare those infected ATMs. The onus is on them to stop this," Bhasin said, without naming the banks.

An SBI branch manager in Pune confirmed that the bank has blocked a few of its customers' cards.

She also said that the bank has sent SMSes to customers informing them that their card was blocked. However, affected customers were largely clueless about this development.

"I had come to Delhi, from Punjab, on Monday and discovered my card was not functioning. When I called the bank, they said I will have to come to Mumbai [my home branch] and re-apply, or transfer my account to Delhi - which will take a fortnight - and then the new card would arrive in seven days," said Ankur Jaiswal, a researcher and SBI account holder.